Bolt mechanism for firearms



Jan. 12, 1960 A. J. LIZZA BOLT MECHANISM FOR FIREARMS 2 Sheets-Sheet 1 Filed Jah. 2, 1958 INVENTORQ Alherl -lLizzu 5. DZAMMQ A. J. LlZZA BOLT MECHANISM FOR FIREARMS Jan. 12, 1960 a 2 Sheets-Sheet 2 Filed Jan. 2, 1958 azz/3% ea '93 as 4 INVENTOR. A1BBT1 J Li z z 11 BOLT MECHANISM FOR FIREARMS Albert J. Lizza, Willimansett, Mass, assignor to the United States of America as represented by the Secretary of the Army Application January 2, 1958, Serial No. 706,880

7 Claims. (Cl. 89-185) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates generally to automatic firearms and more specifically to the bolt mechanisms thereof.

With those firearms which are particularly intended for military use, compactness of structure and ease of assembly and disassembly in the field are features which are especially desired and which are stressed in the designs. in general, there are at the present time two basically different types of bolt systems. In one, the bolt is carried directly by the operating rod and is rotated to lock position when going into battery by lugs extending from the bolt for engagement with integral cam surfaces provided in the receiver. The other is the slide type system wherein a cooperating member is mounted to the bolt for sliding movement relative thereto and is adapted to transfer the energy of an operating member to the bolt and actuate means for locking the bolt in battery during continued forward movement of the sliding member after the bolt stops in battery position.

The advantages of the former type are that the bolt is directly connected at all times to the operating member to provide smooth and positive transfer of movement therebetween. But the disadvantages are that if the operating rod is positioned below the barrel, difficulty arises in the feeding of cartridges from a magazine mounted beneath the ride and disassembly is complicated by the operating rod having to be removed before disassembly of the bolt. If the operating rod is located on the side of the receiver, an opening results in the rear part of the receiver through which dirt may enter to foul the trigger mechanism.

On the other hand, the slide type system facilitates the feeding of cartridges from the underside of the receiver and makes possible a more completely inclosed receiver. Moreover, it provides for a more symmetrical transfer of forces from the operating member to the bolt and is more easily disassembled. However, such a system requires a longer receiverthan that required when a bolt is connected directly to the operating rod as the slide in conventional systems travels beyond the bolt to actuate the locking mechanism and in addition requires a complicated charging device for the proper sequential actuation of the slide and bolt to prepare a firearm for firing. Besides, the slide-bolt assembly is generally unattached to the operating member so that an even force cannot be transferred therebetween. e

It is, therefore, the object of this invention to provide a bolt system for automatic firearms which incorporates the advantages of both the operating rod and slide type bolt systems.

It is another object of this invention to provide a slide type bolt system wherein the bolt is mounted to the slide for rotation therein to a lock position, and does not require additional movement of the slide to effect locking whereby the receiver has the short length of those in firearms having operating rod bolt systems.

2,920,538 Patented Jan. 1 2, 1960 It is a further object of this invention to provide a bolt system wherein the firing pin is locked against accidental actuation until the bolt is rotated to lock position.

It is still a further object of this invention to provide a bolt system suitable for assembly in a box type receiver which provides maximum rigidity with a minimum of weight.

It is a still further object of this invention to provide a bolt system whereby the receiver is completely inclosed when the bolt is in normal battery position to prevent dirt entering the trigger mechanism to cause fouling thereof. r

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which: 1

Fig. 1 is a partially cross-sectioned side view of the firearm shown in battery position; I

Fig. 2 is a view similar to Fig. 1 but showing the firearm in recoil position;

Fig. 3 is a section taken along line 33 of Fig. 2;

Fig. 4 is a view taken along line 4-4 of Fig. 1;

Fig. 5 is a view taken along line 5-5 of Fig. 2;-

Fig. 6 is a partially cross-sectioned top view. of the firearm receiver with the bolt in retracted position; and

Fig. 7 is an exploded view of the slide-bolt assembly shown in perspective.

Shown in the figures is a firearm having a receiver 12 of box type construction whereby maximum rigidity is achieved with a minimum of weight. Such construction is possible because of the unique system hereinafter described which includes a bifurcated operating rod 14, a cylindrical bolt 16 and a slide 18. Receiver 12 is open at the top and the rear part of such opening is inclosed by a cover 20, leaving sufiicient space in the front end for the ejection of the spent cartridge cases withdrawn from the chamber of a barrel 26 by bolt 16. A magazine 22 of conventional design is mounted to the underside of receiver 12 for feeding a supply of cartridges upwardly through a port 24 provided therein.

The front portion of receiver 12, which receives the head portion of bolt 16 when in battery position and is noted at 28, is strengthened by increasing the thickness of the walls thereof with suflicient space beingretained for passage of the head of bolt 16 therethrough. I

Operating rod 14 is disposed for longitudinal reciprocation below barrel 26 and is actuatable from a forward to a rearward position by a conventional gas operated piston (not shown). Operating rod 14 includes a rod portion 30 which is provided with an axial well 32 extending forwardly from the rear end and integral with such rear end is a yoke portion 34 whichis provided with a base portion 36 from which a pair of arms 38 of rectangular cross: section extend rearwardly in parallel relationship. A coil spring 41 is partially received by well 32 with the front end abutting the end of such well and the rear end dis posed for abutment with the front end of receiver 12 so that such spring is compressed during actuation of operating rod 14 to the rearward position thereof for returning the operating rod to the forward position. A guide 41 extends forwardly from the front end of receiver 12 to be received by spring 40 for preventing misalignment thereof when compressed.

The arms 38 extend rearwardly into receiver 12 through accommodating openings 42 which extend from the front end of receiver 12 through front portion 28 to be slidably received by mating grooves 44 provided longitudinally along the length of the inside walls of the sides of the receiver. When base portion 36 is in contact with the 3 front end of receiver 12 the ends of the arms 38 are adjacent the rear end thereof.

Slide 18 is provided with parallel side portions 46 which slidingly engage the inside walls of receiver 12. A bore is provided longitudinally through slide 18 to rotatinglyreceivethe rear portion of bolt 16 so that the head portion thereof projects forwardly for extension through front portion 28 to the breech of barrel 26. The bottom side of slide 18 is recessed by a longitudinal inverted channel 50 which forms longitudinal runners 52 which are slidingly engaged with the bottom, side of receiver 12 to facilitate movement of theslide therealong. Channel 50 is also arranged to interrupt the walls of bore 48 below the lateral diameter thereof to form a longitudinalmou'th portion 54 which provides communication between such channel and bore. Provided partially around bore 48 adjacent the rear end thereof is an arcuate groove 56 which communicates at one end with channel 50. Groove 56 is arranged to slidingly receive a tongue 58 extending radially from therear end of 'bolt 16'whereby such bolt is mountable to slide 18 for rotation but is retained against longitudinal displacement therein. 'When bolt 16 i's'to'be assembled to slide 18,

tongue 58 is aligned with the front end of mouth portion 54 whereby the bolt may be slid rearwardly into bore 58 until such tongue aligns with'groove 56 when by turning'the bolt such tongue is moved into the gfoove and the assembling is completed. Y

An extractor 60 and an ejector (not shown) of con ventional design are mounted to the head portion of bolt 16 and a longitudinal hole 64 is provided axially therethrough to slidingly receive a firing pin 66. Extending diametrically from the head portion of bolt 16 is a pair of locking lugs 68 which are slidingly received by mating guideways 70 which extend forwardly along the inside walls of front portion 28. The guideways 70 are terminated at the front end by vertically disposed locking abutments 72 which are engaged by the locking lugs 68 when bolt 16 is in battery position. Extending upwardly from the left one of the guideways 70 and downwardly from the rightone thereof are locking recesses 74 and 76, respectively, which. slidingly receive the corresponding ones of the locking lugs 68 when bolt 16 is rotated in a clockwise direction after engaging the locking abutment'72 bymeans hereinafter described. Whereby, bolt 16.is locked against longitudinal displacement in battery position. The top of each of the guideways 70 is formed by a. flange which extends inwardly and along the top of the sides of receiver 12. The flanges are formed to include longitudinal grooves 79 for slidingly receiving cover 20. The left one of the flanges, noted at 78, is disposed for sliding engagement with the upper side of the left one of the locking lugs 68 to prevent rotation of bolt 16 in a clockwise direction while being moved forwardly inside the receiver and to prevent upward vertical movement of the head portion of such bolt and so prevent the cocking of slide 18 and a binding thereof by the upward thrust of the cartridges in magazine 22 against the bolt when riding thereover.

. Bolt 16, slide 18 and firing'pin 66 are secured in assembled relationship by a transversely disposed cam bar 80 which also slidingly cooperates with a pair of cam slots 82 in the bolt, as hereinafter described, to provide rotation thereof into lock position. Cambar 80 is also slidingly received by a pairof longitudinal openings 84 through slide 18 and is arranged to extend from both sides thereof to form end portions 88. The end portions '88 are received in mating recesses 90 pro-v vided in the upper sides of the armsl 38 and thereby connect operating rod 14 to bolt 16 for transferring movement .therebetween. The end portions 88 are assembled into the recesses 90 by means of suitable passageways 92 which extend from the top of the sides of receiver 12 to the grooves 44' and such passageways are so disposed longitudinally that the recesses 90 are alignable. with the passageways when operating rod 14 is moved forwardly from the rearward position thereof the distance of the length of such recesses. Whereby, the end portions 88 are secured against displacement in the recesses and the grooves 44 when operating rod 14 changes direction of movement at the rearward position thereof.

The cam slots 82 are provided with longitudinally disposed linear portions 94 along which cam bar 80 is movable during initial movement from forward position and cooperating angular'portions 96v which extend from the rear end of such linear portions' The angular portions 96 are arranged-to cooperate with cam bar 80 for rotating bolt 16 in'a counterclockwise direction to an unlock position during continuedrearward movement of the cam bar and .forrotating such bolt from unlock to lock position during forward movement of the cam bar in the cam slots during counterrecoil movement of operating rod 14. During the forward movement of' operating rod 14 the force thereof is transferred therefrom to the bolt through the engagement of cam bar 80 with the.

front ends of the angular portions 96. However, bolt 16 is prevented from rotating through such engagement by the sliding engagement of the left one of the locking lugs 68 with the flange 78.

Provided in firing pin 66 is an elongated slot 98 which slidingly receives cam bar 80 topermit longitudinal movement thereof relative to the firing pin while maintaining such firing pin against rotational displacement. A tang 100 extends radially from the rear end of firing pin 66 move firing pin 66 to the locked retracted position in arcuate portion 104. Tang portion 100 is assembled into notch 102 by means of a passageway communicating with the right end of arcuate portion 104. Y

A knob 112 is fixed to the right one of the arms 38 so as to extend outwardly'and provide manual means for actuating operating rod 14 to charge the firearm and such knob is slidingly received in an accommodating longitudinal slit (not shown) in the right side of receiver 12. Such jslit is narrower than the supporting one of the arms'38 so as to-be covered thereby to prevent dirt from entering thereci'eiver. t I Operation The belt system-of the present invention is of closed bolt type and thereby bo'lt16 is normally positioned in battery and so covers the front portion of receiver 12 which is not inclosed by cover 20 to prevent dirt from entering the receiver. When the rifle is fired, the resulting gas pressure produced in'barrel 26 causes operating rod 14 to be energized for rearward movement. During the initial portion of'such rearward movement, cam bar 80 is moved by operating rod 14 simultaneously along the openings 84 inslide 18 and the linear portions 94 of the cam slots 82 in bolt 16 and during the -'t1nie of such travel the pressure'of the gases in'barrel 26Iis reduced sufliciently so that the breech thereof may be safely opened. After such dwell period, cam bar 80 engages the angular portions 96 and thereby rotates bolt'16 in a out of the cooperating recesses 74 and 76 and into communication with the guideways f70. Thus, bolt 16 is unlocked and free'to move rearwardly with the operating a rod through the engagement of the cam bar with the rear sides of the angular portions 96. During such rotation of bolt 16 the engagement of angular side 108 therein with tang 100 cammingly moves firing pin 66 rearwardly to extract the point thereof from the primer of the cartridge previously exploded thereby and position such tang portion in arcuate portion 104 of locking notch 102 to prevent discharge of a chamberedcartridge thereby until bolt 16 is rotated to lock position.

Powered by the energy stored in spring 40 during recoil, operating rod 14 with the attached bolt .16 and slide 18 are returned to normal battery position with the end portions 88 first traveling along the grooves 44 and then along the guideways 70 when the bolt approaches battery position. A cartridge is rammed from magazine 22 by bolt 16 on the way to battery POSI- tion and chambered in barrel 26. When bolt 16 reaches battery position, forward travel thereof is stopped by the engagement of the locking lugs 68 with the locking abutments 72. However, operating rod 14 continues to move forwardly through inertia and the energy in spring 40 so that cam bar 80 is moved forwardly along the cam slots 82 in bolt 16 and the openings 84 in slide 18. During the initial movement of cam bar 80 in the cam slots 82, such cam bar slidingly moves along the front walls of angular portions 96, to rotate bolt 16 so that the locking lugs are moved into their respective locking recesses 74 and 76 and thereby lock the bolt against longitudinal displacement, with such cam bar coming to rest in the front end of the cam slot. When bolt 16 is rotated to lock position, locking notch 102 is rotated to bring triangular portion 106 therein into alignment with tang 100 freeing firing pin 66 for actuation by hammer means (not shown) against the chambered cartridge.

From the foregoing, it is seen that there is herein provided a bolt system which incorporates the desirable features of the operating rod and slide types whereby receiver 12 is of short length and of box design and is inclosed to prevent dirt from entering thereinto, bolt 16 is directly connected to the operating rod and ammunition is fed through the bottom of the receiver between the arms 38. Moreover, the system is easily disassembled because with the removal of cover 20 the bolt-slide group is easily removed from receiver 12 when operating rod 14 is moved forwardly to align the recesses 90 with the passageways 92. Withbolt 16 and slide 18 removed from the rifle, such components and firing pin 66 are freed for disassembly as hereinbefore described by the removal of cam bar 80. Further, the bolt system is marked by simplicity of design and ease of manufacture.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

I claim: V

1. In a firearm, the combination of a receiver of rectangular configuration, a magazine disposed for feeding cartridges into said receiver through a port in the bottom thereof, a barrel mounted to the front end of said receiver, an operating rod mounted for reciprocation below said barrel, a pair of arm portions extending rearwardly from said operating rod along the sides of said receiver, a slide mounted between said arms in said receiver for longitudinal nonrotatable reciprocation therein, a bolt mounted in said slide for rotation between a lock and an unlock position and for longitudinal reciprocation with said slide to sequentially transfer cartridges from said magazine to said barrel, a firing pin slidingly mounted in an axial hole through said bolt, a cam bar mounted transversely through said slide, bolt and firing pin to secure such components in assembled relationship and restrain rotation of said firing pin relative to said slide, cam means disposed in said bolt for engagement by said cam bar to convert longitudinal movement thereof relative to said bolt to rotation thereof between the lock and unlock positions, longitudinal openings provided in said firing pin and slide to permit longitudinal movement of said cam bar relative thereto, means for restraining relative longitudinal displacement of said bolt and slide, end portions of said cam bar extending from opposite'sides of said slide for respective engagement with saidarm portions to symmetrically transfer the reciprocation of said operating rod to said cam bar, and means for restraining rotatable movement of said bolt during forward movement thereof until in a battery position so that the energy in said operating rod is transferred directly and symmetrically to said bolt through said cam bar and cam means.

2. The combination of claim 1 and including cooperating tongue and notch means provided respectively on said firing pin and in said bolt for locking said firing pin against longitudinal movement respective to said bolt when said bolt is in the unlocked position.

3. The device of claim 1 and including a longitudinal slot in said firing pin for receiving said cam bar therethrough to restrict rotational movement of said firing pin, a tang extending radially from said firing pin and a notch in said bolt including an arcuate portion for receiving said tang when said bolt is in the unlock position to releasably secure said firing pin in the retracted position, a triangular portion extending from said arcuate portion for alignment with said tang when said bolt is in the locked position to permit movement of said firing pin to the firing position, and an angular side formed by said trangular portion disposed for camming engagement with said tang when said bolt is rotated from the lock to unlock position for moving said tang into said arcuate portion.

.4. In a firearm having a receiver with an attached barrel and a magazine for feeding cartridges through a port in the bottom of-the receiver, an operating rod having a rod portion slidingly disposed below the barrel and a pair of longitudinal arms slidingly received in longitudinal grooves provided along the inside walls of the receiver, a slide mounted for sliding nonrotatable movement within the receiver and provided with a pair of laterally disposed openings, a bolt rotatably carried by said slide and including a pair of diametrically disposed cam slots, a firing pm mounted in said bolt for longitudinal movement between a retracted and a firing position and including a longitudinal slot therethrough, a cam bar mounted transversely through said openings, said cam slots and said longitudinal slot for releasably securing said slide, bolt and firing pin in assembled relationship, end portions of said cam bar extending from both sides of said slide, recesses in said arms for receiving said end portions to transfer movement of said operating rod to said cam bar, cooperating angular portions of said cam slots for receivrng said cam bar when in the rear end of said cam slots to cooperate therewith for rotating said bolt between the lock and unlock positions when said cam bar is moved in and out of said angular portions, means for preventing the rotation of said bolt until in battery position to en gageably transfer forward movement of said operating rod to said bolt through said angular portions, and tongue and groove means provided respectively on said bolt and in said slide for restraining longitudinal'displacement between said bolt and slide while permitting rotation of sla bolt between the lock and unlock positions in said s 1 e.

5. In a firearm, the combination of a receiver of rectangular configuration, a magazine disposed for feeding cartridges into said receiver through a port in the bottom thereof, a barrel mounted to the front end of said receiver, an operating rod mounted for reciprocation below said barrel, a slide mounted for longitudinal nonrotatable movement in said receiver, a bolt, mounted in said slide for rotation between a lock and an unlock position, means cooperatingly interposed between said slide and said bolt to prevent relative longitudinal displacement therebetween, and means for directly connecting said bolt to said operating rod and for rotating said bolt between 

